Etching with vinegar

[Variometer]

I read about this process a couple of days ago. I liked the idea of moving from very corrosive liquids to something less dangerous.
Yesterday evening, I put a small trial piece of PCB and a small square of 2 'thou brass in a tray. I then filled it with a 50-50 mixture of white vinegar and hydrogen peroxide mouthwash (3% strength). This morning, the brass has almost disappeared and the etching process on the copper PCB board is obviously progressing. It takes a long time, but I like the idea of using a safer etching liquid.
Wonder if anyone else has tried this?
Bob

[Ed_Dinning]

Hi Bob, there are a whole range of weak acids that may be suitable, such as citric and tartaric acids. I wondered if Coke would work as it seems to clean coins.
Coke may have the advantage of the CO2 bubbles "agitate" the surface and lead to quicker etching.
One this thought there are available bubble etch tanks, where air is pumped in at low pressure. As this is a low strength acid, how about using the airpump from a fish tank and possibly heat the solution as well.

Ed

[David G4EBT]

I've not tried it Bob, but can see the attraction, though of course the downside is the prolonged etching time, albeit you can walk way from it knowing that nothing untoward is likely to happen. I guess it's a trade-off between the longer time and the reduced risks that are posed. Personally, I prefer to supervise the etching process from start to finish, which I do in the garage or outdoors as weather permits, which is over and done within 15 minutes, and take sensible precautions. A speedy etching time reduces the risk of undercutting on fine tracks by inspecting the PCB at intervals to check progress, and halting the etching as soon as the board has been etched.

I've tried various etchants over the years, having long since abandoned using ghastly ferric chloride. I settled on using Sodium Persulphate clear PCB etchant some years ago and have stuck with it. It has a 6 – 8 minute etch time at 45C – 50C. (above 50C it loses its strength, below 40C it prolongs the etchant time). The bath life is about 4 – 6 weeks depending on use and operating temperature. Unlike ferric chloride with its brown sludge, it leaves no residue – the solution turns pale blue in use. I warm it up with an aquarium heater and check it with an IR thermometer, but you can stand the plastic etchant container in a washing up bowl of boiling water to warm up the etchant. You can use it cold – it just takes longer to work.

To speed up the etching process, I use a 5” long aquarium airstone, which are very cheap, and a small aquarium air pump to bubble the etchant.

I use a plastic cereal container as an etchant bath.

A 500 gram HDPE bottle of Sodium Persulphate copper etchant will make up to 2.5 litres of etching solution, which can be stored for re-use.It's supplied as a fine crystalline white powder, which looks a bit like salt, and instructions for use are printed on the bottle label. It can be found on e-bay, and presently costs £10.49 post free for 500g supplied in a strong HDPE container.

[Variometer]

Thanks for replies. Until now, I have used Sodium Persulphate as well, but it has never completed the etching in ten minutes or so, more like two hours. But I am not generally etching copper clad board, but 2 'thou brass shim. I keep it warm whilst it is etching, but I suppose it just takes longer to etch brass away. I have never tried it on copper board, but may give it a try on my next radio project.
I am still curious as to how my vinegar etching will turn out.
Bob

[Ti Pwun]

Originally Posted by Variometer

Thanks for replies. Until now, I have used Sodium Persulphate as well, but it has never completed the etching in ten minutes or so, more like two hours...

Do you agitate the bath? If you rock it back and forth or make an agitator (slow moving motor and a cam) it will etch much quicker.

Not sure about vinegar. I haven't tried it but it seems like it would take hours to etch a board, probably risking etching under the resist on thin traces because of the length of time it would need to be submerged, but no harm in experimenting.

I used to use Ferric Chloride but now use 1 part Hydrochloric (Muratic) acid poured into 2 parts Hydrogen Peroxide. Still pretty potent chemicals, of course, but it etches quicker and nowhere near as noxious as Ferric Chloride.

[Variometer]

Yes, I did agitate it from time to time, but 2 'thou brass may be thicker than the copper on a PC board.
The vinegar etching is now complete, and it took about 24 hours, but it was successful!
Bob

[David G4EBT]

I'd agree about some for of agitation, which is why I use an aquarium air stone and pump to bubble the etchant. My main concern with a longer etching time on PCBs with lots of narrow, densely packed tracks, would be the risk of undercutting the tracks if the board is left in the bath for prolonged period. A quick etching time, and removing the PCB just a soon as all tracks have been etched, minimises the risk of that.

I've attached a couple of pics of PCBs I etched some years ago when still interested in amateur radio. One is 3" x 2", for a miniature low power CW transceiver for 40 Metres, known as the NORCAL (Northern California) '49er' - the other is 4.5" x 1.5" and is for an SSB/CW QRM audio filter using three quad op amps (12 stages in total). As will be seen, on both PCBs the tracks are quite narrow & close together, so would soon be undercut without being vigilant when etching. Making PCBs is fiddly, time consuming and hit & miss enough as it is, without risking failures.

The other pic is of a PCB I etched this week and have since populated. It's for a 20Hz - 22kHz sine wave generator, for which the PCB is much less critical - 5" square, with fewer and wider tracks and just one op-amp. I enjoy building simple test gear, which I'm afraid I tend to do impulsively whether I need it or not. I don't need yet another waveform generator, but I liked the simple design so my lack of self-discipline caused me to be needlessly distracted from other half-finished projects to knock up this generator, which now needs boxing up and calibrating.

I think the same can be said for slow/fast etching as can be said for exposing UV boards. I've heard people say you can do it without a light-box by placing it in sunlight for hours on end, to let the sun's UV rays go to work on it, and I don't doubt that is so, but I prefer a controlled, timed process and which relaying on the variability (or non existence!) of sunlight when there are excellent simple designs for cheaply made UV exposure units using a bank of high brightness UV LEDs, albeit I have a homebrew light-box anyway.

It's good fun to experiment and I wouldn't write off or denigrate any ideas - after all, that's what we're about!

I wonder what the reaction was to the first guy who said 'I've got an idea - what about designing a 3-D printer to print plastic objects?' Huh - do what?

Good luck with your etching experiments Bob.

[Variometer]

I have been etching for a number of years now, but have always found it a bit of "hit & miss!" Sometimes, the whole thing is a complete failure, and other times, near perfect. I mainly etch from 2 'thou brass shim, using Sodium Persulphate. I have tried photo etching and that has been 90% failure
I could never coat the brass evenly. No matter how clean the brass was, and how dust-free the air appeared to be, the coating always had little raised lumps on it, apparently with a speck of dirt in the middle of each! Gave up in the end!

PCB pens never work for me, despite being told to use this that or the other types, that have always given others perfection.

My present method that is pretty good, is to put the pattern on the brass with a PCB pen. Then, after it is dry, stick strips of "Magic" Scotch Tape over the lines. In order to make the tape more visible, I black the top with a marker pen. I then roll it firmly on with a wallpaper roller.

If I put too much chemical in, the whole lot disappears, so now, I tend to use about 3 teaspoonfuls to 300ml of water. Agitate gently every ten minutes or so. This method takes about two hours, but I am getting quite good at it now. Here is my latest (nothing to do with radio), although I do a lot of Homebrew radio work!

Th vinegar was just an experiment, and I may try something more ambitious with it, maybe when we are going out all day, and can just leave it to its own devices. It does take an awful long time though!

Bob

[dseymo1]

Ingenious - I'd never have thought of producing a grille using a subtractive method!

Edit: the above might sound sarcasic, but is meant sincerely

[Bazz4CQJ]

Originally Posted by Variometer

PCB pens never work for me, despite being told to use this that or the other types, that have always given others perfection.

Curious! I've always found the Dalo pens work splendidly; from the one I bought back in the early 70's to the one I bought a few months ago. But I always stick with ferric chloride etchant, though it's hard to believe that using persulphate or vinegar would affect those pens, which use a particularly suitable ink.

B

[Ti Pwun]

This thread reminds me of the days when I would sit down for hours with lettraset transfers and a pencil. I also had success with the pens but I do remember that if I didn't draw slowly I would end up with minute gaps along the length of some traces, often unseen until the board was etched.

Thank heavens for laser printers, acetate, UV exposure units, Muriatic acid, Hydrogen Peroxide, tinning powder...

...and the Internet, of course...

...none of which I had access to when I was making boards as a youngster. Happy days, though. Even the image of that yellow/brown stain on my bedroom carpet brings a smile when I think back to those days...

24 hours to etch with vinegar is a long wait. I hated the wait involved with Ferric Chloride but a whole day would be a killer. I've known of people etching patterns on knife blades using vinegar but I wouldn't have thought of using it for removal of anything but the surface layer. Interesting experiment.

I love using the chemicals I use now because it etches a PCB in next to no time. Doesn't have a shelf life so I make it up as I need it but it is nice to work with.

[Wendymott]

Hi Peeps... May I add my "two pennorth" to this.... I have been making pcb's on and off for most of my working life, and as is the norm in "work conditions" speed was of the essence, thus Ferric Chloride was and is always used with an air agitator. I know its not part of the original question, but the most practical. My latest setup, as I am no longer making boards professionally, is a "Maplin" tank, made of Thick glass and a plastic frame, with a "fishtank" aireator. The problem with the original supplied aireator, was it used to bung up with sediment, quite quickly, so recently I replaced with a piece of polythene pipe, but the drilling of the holes is quite important. If they are all the same size, say 1mm..only the feed end will bubble....so I scaled the holes..from the feed end, 0.6mm to 1.2mm at the closed end at a gap of approx. 20 mm between holes. This distributes the air pressure, reasonably evenly so I get a decent curtain of bubbles right across the tank.
With the fluid at 20 deg C my pcb's etch in about 10 - 12 mins................. I agree that Ferric is a nasty chemical, but handled carefully, need not be too much of a negative experience. Fortunately my system is in the basement with a pot sink nearby.
Interesting though ..the thought of using less nasty fluids, but when I am wanting a pcb, it like "NOW" not sometime soon.

[David G4EBT]

Commercial tanks seem ridiculously expensive and seem not to confer any advantages for DIY PCB production. (IE: unheated tank from Maplin, presently £170).

My 'tank' is a cereal container from Poundland and the aerator is a five inch aquarium airstone which costs less than a pound and works very well. Air-pumps are under £10.00, as are heaters - available up to 200 Watts. However, most aquarium heaters are thermostatic these days (for obvious reasons!) and the upper temperature is generally 34 degrees C, whereas etchant ideally needs to be 45 - 50C. (Maybe the thermostats can be shorted out to disable them?). I've had my heater for some years and it's non-thermostatic. I use a sink drainer (Poundland again!) cut to size to cradle the PCB in the tank so I can lift it up from time to time to check etching progress.

As to Ferric Chloride, my main objection that caused me to abandon it about 12 years ago, isn't that it's 'nasty' in the hazardous sense - it's purpose in life is to be corrosive, so by definition it poses hazards, as do the alternatives (apart from vinegar of course, which is the subject of the thread). I went over to sodium persulphate because it's transparent and leaves no sludge or stains, yet is just as effective. All that happens is that in use, it turns light blue. Every bit as quick as Ferric chloride with none of the downsides.

I guess that whatever alternative methods we each use, all that really matters is that it's consistently successful rather than hit and miss.

I must say that the results that Bob has attained using vinegar - without the paraphernalia of heater, pump and aerator - are impressive.

I've attached a pic of my cheapo but effective set-up.

[G6Tanuki]

I've always - and still do - use the traditional Ferric Chloride. It's cheap, quick and efficient: what more do I need? [I don't put the used etchant down my drains though - it could mess-up the septic tank's biology].

Most of the PCBs I've done have been small - 3 inches square - for things like VHF preamps or low-power LM380/TBA820 audio-amps. I use a 1-litre plastic ice-cream container as the etch-bath.

As a resist I use nail-varnish painted on by hand with a really-thin paintbrush: my local drug-store often has a basket of 'out-of-fashion' nail-varnish colors for 50p a time. If you're doing double-sided PCBs you can easily etch one side at a time by cutting notches in four corks and fitting them on the corners of your board as 'buoyancy aids' to stop it sinking.

Professionally - I outsource the entire job! if only because I can sue them if they fail.

[Ed_Dinning]

Hi Folks, when I worked as an EO at a university which had a chemistry department we used Chromic acid as the etchant that was sprayed onto the board through a very fine nozzle, all done in a fume cupboard with a fireproof floor. It went pretty quickly, but that was a nasty chemical, far worse than acidified ferric chloride.

Ed

[Mike Phelan]

Etching PCBs was never my favourite occupation. I've always used ferric chloride in a plastic tub surrounded by a dish of boiling water, with the print side uppermost.

I've tried a few ways of doing the resist: Dalomark etch-resist pens never worked for me so I gave up with those; light-sensitive PCBs, too much faffing about getting the time just right.

Best I could do was to stick Fablon on and cut away the required print side followed by a shellac coating for the resist; pull Fablon off, leave resist to dry overnight and etch.
Reasonable results.


Ed's chromic acid - I had some once and used it to give the finish on brass that you find on new 13A plug pins. No corrosion for decades but horrendous stuff.

I've seen some of David's PCBs and they look superb. Probably hear and aeration are the secret.

[Ti Pwun]

Originally Posted by Wendymott

...Fortunately my system is in the basement with a pot sink nearby...

Oh, to have an old pot sink nearby! I use a heavy duty plastic drum to store what little waste I can't recycle but I did recently pour a small quantity of Hydrochloric acid into a container over the stainless steel kitchen sink (newly installed) and a little bit of it splashed into the sink.

Stainless steel definitely isn't stainless! Ask the wife - she will confirm. Eek!

[Ti Pwun]

Originally Posted by Mike Phelan

...I gave up with those; light-sensitive PCBs, too much faffing about getting the time just right...

I have UV exposure unit and print my board designs on acetate, which I'm used to working with and the results are consistent, but I know what you mean - it was always a hit and miss process before I started doing it the way I do it now.

[Wendymott]

All very interesting.... that's what is great about this group/forum,, so many differing ideas....I agree David G4EBT.... the mechanics such as tanks are stupid prices... my Maplin tank cost £20, it was a return and I bought as a non saleable item... " I worked in the returns dept"... Some time ago the seals went, so I stripped the glass surfaces, made a jig and re glued using proper glass adhesive........ still water tight..
I did not realise the best temp was 50 deg C, I always used 20 deg C, but I still get a typical etch time of 10 Mins.... if it is too quick you can get "undercut", and with SMD devices, you don't want the thin tracks to become non existent..
I always use photo resit material, but the problem is exposure....my artwork base material is clear acetate by Nobo, but the laser printer does not deposit enough onto the acetate, thus I make two copies and make a double density artwork. I have a 3M uv light source with a timer adjustable from 20 - 60 seconds.... but with SMD arts I always do a test piece. I found the process is much the same as photography, many variables, so to try and standardise as mush as possible I have lots of "postits" on the wall.

[Oldcodger]

I've never used anything but ferric chloride as echant. I've never found it a long job, using an old ice cream tub in a sink of hot water and making the etchant move over the board by moving the tub. I've used Dalo pens /transfers and even permanent markers. On one occasion I made a Rolf Harris style xylophone by tracing the keyboard layout through carbon paper on to the copper. I then used a coat of mrs discarded nail varnish (sort of clear) to cover the area and then pick out the gaps between the keys with a nail . Gave a nice well defined PCB. At one time, nail varnish was available in a marker pen format .I did ask mrs to look out for one after this nice board, but it seemed to vanish off the market.